Study co-authored by company finds drivers inevitably take home about the same earnings whether fares go up or down

Hours before Uber Technologies Inc.’s chief executive resigned in June, the ride-hailing company announced a six-month goodwill effort to ease its strained relationship with drivers, who have long sought better work conditions and higher pay.

Since then, Uber has unleashed a host of goodies, including extra payments for lengthy wait times, routing improvements and in-app tipping.